The present invention relates to a screen printing apparatus, screen printing method, and paste storage container used for the screen printing apparatus. More particularly, it relates to a screen printing method to print cream solder or conductive paste on a substrate or the like, and a paste storage container used for a screen printing apparatus.
In a conventional electronic parts mounting process, a screen printing has been employed as a method to print cream paste, conductive paste or like paste on a substrate. Such conventional screen printing method comprises a step of setting a mask plate on a substrate wherein the mask plate has pattern holes formed according to the printing portions, and a step of printing a paste on the substrate through the pattern holes in the mask plate by squeezing.
As a squeezing method in such conventional screen printing, a method of using a closed-type squeegee head is well-known. In this method, unlike an ordinary screen printing method, the paste is not directly supplied onto the mask plate, but a squeegee head which stores the paste is installed in the printing apparatus. In such method of using a closed-type squeegee head, unlike a conventional printing method in which the paste is directly supplied onto the screen mask, the paste is supplied in a state of being stored in a storage container such as a cartridge in the squeegee head. And, the paste in the cartridge is pressurized and pushed out. The squeegee head slides on the mask plate while being in contact with the mask plate, and thereby, the paste is filled into each pattern hole sequentially. In the conventional method, a container having an opening to push out the paste at the bottom is used as a cartridge. Inside the container, a pressure plate disposed free to move up and down is pressed, then the paste is gradually pushed out of the opening at the bottom.
However, the paste storing cartridge used for the conventional closed-type squeegee head has problems as described in the following.
Generally, a paste like cream solder is adhesive and hard to flow, and furthers has a characteristic such that the cream solder changes in property with the lapse of time. Accordingly, it has been difficult to push out the paste from the opening smoothly at a specified pressure by utilizing the change in fluidity of the paste when the pressure plate is pressed by the specified pressure.
Also, using the conventional storage container, it is difficult to completely push out and use up the paste. Accordingly, there has been generated much paste unused and discarded, resulting in wasting the material.
The present invention is intended to provide a screen printing apparatus, screen printing method, and paste storage container for the screen printing apparatus, by which the paste can be reliably pushed out and completely used at all times without wasting the material.
A screen printing apparatus to print a paste on a substrate of the present invention comprises:
(a) a positioning section which holds the substrate;
(b) a mask plate having pattern holes, where the mask plate is disposed above the substrate;
(c) a squeegee head to store and supply the paste onto the mask plate; and
(d) a pressure mechanism to pressurize the paste in the squeegee head,
wherein the squeegee head includes a paste storage container to store the paste and a printing space to accommodate the paste supplied from the paste storage container;
the paste storage container has a volume-variable container which varies in volume according to the operation of the pressure mechanism;
the volume-variable container has through-holes; and
the volume-variable container is reduced in volume according to the operation of the pressure mechanism, and the paste filled in the volume-variable container is pushed out into the printing space through the through-holes, and thereby, the paste is supplied onto the mask plate.
A screen printing method of the present invention comprises:
(a) a step of preparing a squeegee head having a volume-variable container and a printing space,
where the volume-variable container includes a projecting portion with projections, side wall, and push-out plate with through-holes, and
the printing space is communicated to the push-out plate;
(b) a step of storing a paste in the volume-variable container;
(c) a step of pressurizing the projecting portion and also pushing out the paste into the printing space through the through-holes while compressing the interior of the volume-variable container;
(d) a step of continuously pressurizing the projecting portion so that the projections fit into the through-holes, thereby pushing out the paste remaining in the through-holes into the printing space; and
(e) a step of supplying the paste pushed out into the printing space onto the mask plate to print the paste on a substrate via the mask plate.
Preferably, the volume-variable container includes a push-out plate which forms the bottom of the volume-variable container, and the push-out plate has a plurality of through-holes, and the paste is pushed out into the printing space through the through-holes.
Preferably, the volume-variable container further includes a free-to-move projecting portion, and the projecting portion has a plurality of projections which may fit into the through-holes, and according to the operation of the pressure mechanism, the projecting portion moves to push out the paste in the volume-variable container into the printing space through the through-holes, and then the projections fit into the through-holes to push out the paste remaining in the through-holes into the printing space.
By the above configuration, the paste being stable in viscosity is pushed out into the printing space. Further, the paste stored in the paste storage container can be completely pushed out into the printing space without remaining in the paste storage container.